Here is below my Xcode IDE project folder structure:
WebService This folder contains all web service classes and routers. It also contains web service error handlers
ViewModel This folder contains all business logical classes
View This folder contains all UITableviewCell, UICollectionViewCell or other UI related classes with meaninful related folder.
Controllers This folder as the name suggest contains all controller classes and again it should named excat same or similar naming with view models or views and models.
DataSource Mainly I put all of models items in a datasource for to use in TableViews and UICollectionViews. This makes my controller more lighter and reasuable.
Extensions This folder contains all of the extend classes for example UIColors, Strings, Collections etc. whatever I need to extend I put this folder with a meaningful folder name
Externals Mainly this folder only contains JSON, Fonts, Audio or Video files.
UI This folder only contains Storyboards, XCAssets or Xib files. I always separate Storyboard for different module to make it easier to work with in a team. For example: UserProfile.storyboard, ProductList.storyboard etc.